Re: [PATCH 10/13] arm: uncompress: verify sha256 if enabled

[Sascha Hauer <s.hauer@pengutronix.de>]

On Mon, Jul 01, 2019 at 08:19:13AM +0200, Rouven Czerwinski wrote:
> On Wed, 2019-06-26 at 09:52 +0200, Sascha Hauer wrote:
> > On Wed, Jun 26, 2019 at 06:58:51AM +0200, Rouven Czerwinski wrote:
> > > Add piggydata verification before the ARM uncompress function.
> > > This calculates the sha256sum of the compressed barebox binary and
> > > only
> > > continues if the builtin sha256sum matches the calculated
> > > sha256sum.
> > > 
> > > Signed-off-by: Rouven Czerwinski <r.czerwinski@pengutronix.de>
> > > ---
> > >  arch/arm/cpu/uncompress.c | 18 +++++++++++++++++-
> > >  1 file changed, 17 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/arch/arm/cpu/uncompress.c b/arch/arm/cpu/uncompress.c
> > > index e527165..ce5f2c1 100644
> > > --- a/arch/arm/cpu/uncompress.c
> > > +++ b/arch/arm/cpu/uncompress.c
> > > @@ -42,14 +42,18 @@ unsigned long free_mem_end_ptr;
> > >  extern unsigned char input_data[];
> > >  extern unsigned char input_data_end[];
> > >  
> > > +extern unsigned char sha_sum[];
> > > +extern unsigned char sha_sum_end[];
> > > +
> > >  void __noreturn barebox_multi_pbl_start(unsigned long membase,
> > >  		unsigned long memsize, void *boarddata)
> > >  {
> > > -	uint32_t pg_len, uncompressed_len;
> > > +	uint32_t pg_len, uncompressed_len, pbl_hash_len;
> > >  	void __noreturn (*barebox)(unsigned long, unsigned long, void
> > > *);
> > >  	unsigned long endmem = membase + memsize;
> > >  	unsigned long barebox_base;
> > >  	void *pg_start, *pg_end;
> > > +	void *pbl_hash_start, *pbl_hash_end;
> > >  	unsigned long pc = get_pc();
> > >  
> > >  	pg_start = input_data + global_variable_offset();
> > > @@ -92,6 +96,18 @@ void __noreturn barebox_multi_pbl_start(unsigned
> > > long membase,
> > >  	pr_debug("uncompressing barebox binary at 0x%p (size 0x%08x) to
> > > 0x%08lx (uncompressed size: 0x%08x)\n",
> > >  			pg_start, pg_len, barebox_base,
> > > uncompressed_len);
> > >  
> > > +	if (IS_ENABLED(CONFIG_PBL_VERIFY_PIGGY)) {
> > > +		pbl_hash_start = sha_sum + global_variable_offset();
> > > +		pbl_hash_end = sha_sum_end + global_variable_offset();
> > > +		pbl_hash_len = pbl_hash_end - pbl_hash_start;
> > > +		if (pbl_barebox_verify(pg_start, pg_len,
> > > pbl_hash_start,
> > > +				       pbl_hash_len) != 0) {
> > > +			putc_ll('!');
> > > +			pr_err("hash mismatch, refusing to
> > > decompress");
> > > +			panic("hash mismatch, refusing to decompress");
> > 
> > Isn't printing the string in panic() enough?
> 
> Unfortunately not, pbl/misc.c defines panic as:
> 
> void __noreturn panic(const char *fmt, ...)
> {
> 	while(1);
> }

Then maybe we should add the printf here. We have static inline wrappers
for printf when the cosnole is disabled in the PBL.

Sascha

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